The present invention relates to a method and apparatus for measuring and monitoring the angular velocity of the shaft of a rapidly rotating machine.
The regulation of a machine which rotates at high speeds, such as a turbine, requires the constant reliable monitoring of its angular velocity and the indication in revolutions per unit time of deviations from the desired speed. In order to utilize speed proportional signals for such purposes, magnetic and optical sensors are known which are actuated by the passage of special reference markers attached to the machine shaft. For example, a frequently used system includes a toothed disc which is fastened to the machine shaft and which has teeth uniformly distributed over its circumference. Inductive sensors disposed opposite the teeth convert the passage of each tooth into a voltage pulse which is converted into a signal proportional to the speed of the machine.
A speed measuring device is disclosed in German Pat. No. 1,223,179 for the evaluation of such pulses. In this prior art arrangement, a pulse generator furnishes pulses having a pulse repetition rate which is proportional to the actual number of revolutions of the rotating machine to a pulse counter. However, this device does not indicate speed in revolutions per minute (rpm), and the single channel circuit provided does not meet present-day requirements for measurements that are accurate enough to be used in regulating devices.
Accordingly, it is an object of the invention to provide a method and apparatus of the above-mentioned type wherein a highly reliable measurement is obtained from pulse sequences having a pulse repetition rate or frequency proportional to the number of revolutions of a rotating machine, the effect of malfunctions in the speed detection device is minimized and which provides a direct indication of the speed of the machine in revolutions per minute. The invention is particularly suitable for high speed machines having angular velocities on the order of about 10,000 revolutions per minute.